Avidin self‐associates with boric acid gel suspensions: preparation of an affinity boron carrier that might be developed for boron‐neutron capture therapy

Abstract

AbstractIt has been shown in preliminary studies that avidin self‐associates with suspended arylboronic acid gel polymer particles, and avidin‐coated gel particles in the micron and submicron size range are of interest to boron‐neutron capture therapy (BNCT) applications because they carry sufficiently large amounts of boron‐10 to effect a meaningful tissue dosing through BNCT. Avidin‐coated gel particles precipitate within 46 min of mixing when the avidin/colloid ratio is about 0.34 g avidin/g colloid. This is a minimum time if gel and avidin concentrations are in the low microgram/milliliter range, and further increases in the relative amount of avidin increase the time to precipitation. At shorter exposure times rapid agglutination‐like reactions were observed with multivalent biotinylated bovine albumin, suggesting that two stage pre‐targeting of specific tissues should be possible with biotinylated antitumor antibodies. The yield of micron sized and smaller gel particles is enhanced by a combination of manual grinding in an agate mortar followed by sonification. Sonification alone produces an uneven distribution, with fewer particles sedimenting at 15 000 rpm than above or below. Preparation of avidin‐coated boronic acid particles is a matter of combining a phosphate buffered solution of avidin (120 mM in NaCl, 2.7 mM in KCl and 10 mM in phosphate, pH 7.4) and an aqueous suspension of gel particles in the mass ratio described above. Copyright © 2005 John Wiley & Sons, Ltd.